Dual metal for a backside package of backside illuminated image sensor

ABSTRACT

A method for fabricating a semiconductor device with improved bonding ability is disclosed. The method comprises providing a substrate having a front surface and a back surface; forming one or more sensor elements on the front surface of the substrate; forming one or more metallization layers over the front surface of the substrate, wherein forming a first metallization layer comprises forming a first conductive layer over the front surface of the substrate; removing the first conductive layer from a first region of the substrate; forming a second conductive layer over the front surface of the substrate; and removing portions of the second conductive layer from the first region and a second region of the substrate, wherein the first metallization layer in the first region comprises the second conductive layer and the first metallization layer in the second region comprises the first conductive layer and the second conductive layer.

This application is a continuation of U.S. Ser. No. 12/356,968 filedJan. 21, 2009, and entitled, “Dual Metal For A Backside Package ofBackside Illuminated Image Sensor,” the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND

An image sensor provides a grid of pixels, such as photosensitive diodesor photodiodes, reset transistors, source follower transistors, pinnedlayer photodiodes, non-pinned layer photodiodes, and/or transfertransistors, for recording an intensity or brightness of light. Thepixel responds to the light by accumulating a charge—the more light, thehigher the charge. The charge can be processed by another circuit sothat a color and brightness can be used for a suitable application, suchas a digital camera. Common types of pixel grids include acharge-coupled device (CCD) or complimentary metal oxide semiconductor(CMOS) image sensor.

Backside illuminated sensors are used for sensing a volume of exposedlight projected towards a back surface of a substrate. Backsideilluminated sensors provide a high fill factor and reduced destructiveinterference, as compared to front-side illuminated sensors. The pixelsare located on a front side of the substrate, and the substrate is thinenough so that light radiation projected towards the backside of thesubstrate can reach the pixels. Due to the thinned substrate, asupplemental device (e.g., a carrier wafer) is typically attached to thefront surface of the substrate on which one or more sensor elements arefabricated. Since such supplemental devices block or prevent readyaccess to the bond pads of individual sensor elements, the back surfaceof the substrate is often processed to form an opening providing accessto bond pads of the individual sensor elements. It has been observedthat bondability to these bond pads is inadequate. Various methods havebeen introduced to improve bondability by increasing the thickness ofthe bond pad layers where the bonding occurs; however, such methods arecostly, often complicate processing, and/or decrease sensor elementperformance.

Accordingly, what is needed is a method for manufacturing a backsideilluminated sensor device that addresses the above stated issues.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a flow chart of a method for fabricating a semiconductordevice according to aspects of the present invention.

FIGS. 2A-2N are various cross-sectional views of embodiments of asemiconductor device during various fabrication stages according to themethod of FIG. 1.

DETAILED DESCRIPTION

It is understood that the following disclosure provides many differentembodiments, or examples, for implementing different features of theinvention. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Forexample, the formation of a first feature over or on a second feature inthe description that follows may include embodiments in which the firstand second features are formed in direct contact, and may also includeembodiments in which additional features may be formed between the firstand second features, such that the first and second features may not bein direct contact. In addition, the present disclosure may repeatreference numerals and/or letters in the various examples. Thisrepetition is for the purpose of simplicity and clarity and does not initself dictate a relationship between the various embodiments and/orconfigurations discussed.

With reference to FIGS. 1 through 2N, a method 100 and a semiconductordevice 200 are collectively described below. FIG. 1 is a flow chart ofone embodiment of the method 100 for making the semiconductor device200. FIGS. 2A-2N are various cross-sectional views of the semiconductordevice 200 according to one embodiment, in portion or entirety, duringvarious fabrication stages of the method 100. It is understood thatadditional steps can be provided before, during, and after the method100, and some of the steps described below can be replaced oreliminated, for additional embodiments of the method. It is furtherunderstood that additional features can be added in the semiconductordevice 200, and some of the features described below can be replaced oreliminated, for additional embodiments of the semiconductor device 200.The present embodiment of method 100 and semiconductor device 200provide improved bonding ability.

Referring to FIGS. 1 and 2A, the method 100 begins at step 102 wherein asubstrate 210 having a first region 211A, a second region 211B, and oneor more sensor elements 212 is provided. In the present embodiment, thesubstrate 210 is a semiconductor substrate. The semiconductor substrate210 may comprise an elementary semiconductor including silicon orgermanium in crystal, polycrystalline, or an amorphous structure; acompound semiconductor including silicon carbide, gallium arsenic,gallium phosphide, indium phosphide, indium arsenide, and/or indiumantimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs,AlGaAs, GaInAs, GaInP, and/or GaInAsP; any other suitable material;and/or combinations thereof. In one embodiment, the alloy semiconductorsubstrate may have a gradient SiGe feature in which the Si and Gecomposition change from one ratio at one location to another ratio atanother location of the gradient SiGe feature. In another embodiment,the alloy SiGe is formed over a silicon substrate. In anotherembodiment, a SiGe substrate is strained. Furthermore, the semiconductorsubstrate may be a semiconductor on insulator (SOI) or a thin filmtransistor (TFT). In some examples, the semiconductor substrate mayinclude a doped epi layer or a buried layer. In other examples, thecompound semiconductor substrate may have a multilayer structure, or thesilicon substrate may include a multilayer compound semiconductorstructure. Still, in other examples, the substrate 210 may comprise anon-semiconductor material.

The substrate 210 may include various doping configurations depending ondesign requirements as known in the art (e.g., p-type substrate regionsand/or n-type substrate regions). In some embodiments, the substrate 210may include doped regions. The doped regions may be doped with p-type orn-type dopants. For example, the doped regions may be doped with p-typedopants, such as boron or BF₂; n-type dopants, such as phosphorus orarsenic; and/or combinations thereof. The doped regions may be formeddirectly on the semiconductor substrate, in a P-well structure, in aN-well structure, in a dual-well structure, or using a raised structure.The substrate 210 may further include one or more lateral isolationfeatures to separate various devices formed on the substrate. The one ormore isolation features may utilize isolation technology, such as LOCOSor STI, to define and electrically isolate the various regions. Theisolation regions may be formed by any suitable process and may comprisesilicon oxide, silicon nitride, silicon oxynitride, fluoride-dopedsilicate glass, a low-K dielectric material, other suitable materials,and/or combinations thereof.

Further, the substrate 210 comprises a front surface and a back surface.In the present embodiment, the semiconductor device 200 is a backsideilluminated sensor device. The semiconductor device 200 is designed toreceive light directed towards the back surface of the substrate 210during applications, eliminating other objects such as gate features andmetal lines from obstructing optical paths and maximizing the exposureof the light-sensing region to the illuminated light. The substrate 210may be thinned such that the light directed through the back surfacethereof may effectively reach the sensor elements 212. The substrate 210includes the first region 211A and the second region 211B, whichcomprise active and/or passive regions. For example, the first region211A comprises an integrated circuit device region and/or main chiparea, wherein various integrated circuit devices may be formed; and thesecond region 211B comprises a test region (or area), wherein the testarea may be disposed in the scribe line and frame areas of semiconductordevice 200 for testing and monitoring during and/or after thefabrication thereof. It is understood that the semiconductor device 200may comprises a plurality of first and second regions 211A, 211B.

The semiconductor device 200 includes one or more sensor elements 212formed on the front surface of the substrate 210. In one embodiment, thesensor elements may be disposed over the front surface and extended intothe substrate 210. The sensor elements 212 each may comprise alight-sensing region (or photo-sensing region) which may be a dopedregion having n-type and/or p-type dopants formed in the semiconductorsubstrate 210 by a method such as diffusion or ion implantation. Thesensor elements 212 may include photodiodes, pinned layer photodiodes,non-pinned layer photodiodes, reset transistors, source followertransistors, transfer transistors, select transistors, complimentarymetal-oxide-semiconductor (CMOS) image sensors, charged coupling device(CCD) sensors, active pixel sensors, passive pixel sensors, othersensors diffused or otherwise formed in the substrate 210, other activeand/or passive features configured and coupled to provide properfunctions such as imaging and/or sensing, and/or combinations thereof.As such, the sensor elements 212 may comprise conventional and/orfuture-developed image sensing devices. The sensor elements 212 maycomprise a plurality of pixels disposed in a sensor array or otherproper configuration. The plurality of sensor pixels may be designedhaving various sensor types. For example, one group of sensor pixels maybe CMOS image sensors and another group of sensor pixels may be passivesensors. Moreover, the sensor elements 212 may comprise color imagesensors and/or monochromatic image sensors. Additional circuitry andinput/outputs are typically provided adjacent to the sensor elements 212for providing an operation environment for the sensor elements 212 andfor supporting external communications with the sensor elements 212. Forexample, the sensor elements 212 may further comprise or be coupled tocomponents such as an electric circuit so that the sensor elements 212are operable to provide a proper response to illuminated light. In someembodiments, each of the sensor elements 212 may be configured tocorrespond with specific light wavelengths, such as a sensor element forsensing a red light wavelength, a sensor element for sensing a greenlight wavelength, and a sensor element for sensing a blue lightwavelength.

Conventional processing continues by forming a plurality of dielectriclayers and a plurality of conductive features including a plurality ofmetal structures coupled to a plurality of contact and/or via structuresover the front surface of the substrate. The plurality of metalstructures and the plurality of contact/via structures may be formed inan integrated process, such as a damascene process or a dual damasceneprocess, and further, vertical and horizontal features may be formed invarious processes, such as photolithography and etching processes. Theplurality of metal structures are typically formed in N metallizationlayers over the front surface of the substrate, where the metalstructures formed directly above the front surface of the substrate areformed in the metal one metallization layer, M1, and the topmost metalstructures are formed in the topmost metallization layer, M(N).

Then, one or more bonding pads may be formed and coupled to at least oneof the M1,metallization layers in a testing region of the substrate,such as the M1 metallization layer. The metallization layer that thebonding pad is coupled to typically comprises a uniform thickness in thetesting region (e.g., second region 211B) and the integrated circuitdevice region (e.g., first region 211A). However, to achieve improvedbonding ability, the bonding pad desirably couples to a metallizationlayer with an increased thickness as compared to the thickness of themetallization layers in the integrated circuit device regions. Severalapproaches are utilized to achieve improved bonding ability. In oneapproach, the semiconductor device is etched back to M1,the M1metallization layer in the testing region; an additional conductivelayer is deposited over M1,the M1 metallization layer in the testingregion, wherein the M1 metallization layer in the testing M1,region thencomprises the M1 metallization layer material found in the integratedcircuit device region plus the additional conductive layer; and abonding wire extending from the back surface M1,of the semiconductordevice to the M1 metallization layer in the testing region is formed.This approach often requires at least two additional masks to patternand etch the testing regions, resulting in increased costs and increasedprocessing difficulties. A second approach involves etching thesemiconductor device back until a metallization layer with an increasedthickness is M1,reached. For example, the process may etch back to aninter-metallization layer, such as a M2 metallization layer or a topmostM(N) metallization layer. However, the inter-metallization and/ortopmost metallization layers are not necessarily thick enough, and thelikelihood of device failure increases since a bonding wire may easilytouch the side-wells and induce leakage from the substrate. Further, thesecond approach is more difficult, presents increased costs, and mayM1,require multiple etching processes. A third approach provides auniform M1 metallization layer with an increased thickness in both thetesting region and the integrated circuit device region; however, theincreased thickness in the integrated circuit device region decreasessensor device performance, which may result from stray capacitance.

Accordingly, the present embodiment provides a method wherein themetallization layer in the testing area (e.g., second region 211B) iseasily made thicker than the metallization layer in the integratedcircuit device area (e.g., first region 211A). The thickness of the M1metallization layer in the testing region is increased, while the M1metallization layer in the integrated circuit device region remains itsoriginal thickness. Specifically, in the present M1,embodiment, the M1metallization layer in the second region 211B is thicker than the M1metallization layer in the first region 211A. The disclosed embodimentsprovide one or more of the following advantages: (1) improved backsideilluminated sensor package yield; (2) improved backside illuminatedsensor bonding ability; (3) improved sensor device (i.e., pixel)performance; (4) decreased cost; (5) easily integrated into existingdevice processing; and (6) easily extends to next generation processes.

M1,Referring to FIG. 1 and FIGS. 2B-2K, a first metallization layer M1is formed over the front surface of the substrate 210. In the presentembodiment, an inter-layer (or level) dielectric (ILD) layer 214 isformed over the front surface of the substrate 210 as illustrated inFIG. 2B. The ILD layer 214 comprises a low-K (LK), ultra low-K (ULK),extra low-K (ELK), and/or XLK material. The material classification isbased upon capacitance or k value, with LK usually referring to thosematerials with a k between about 3.1 to 2.7, ULK usually referring tothose materials with a k between about 2.7 to 2.4, ELK usually referringto those materials with a k between about 2.3 to 2.0, and XLK referringto those materials which typically have a k value less than about 2.0.The LK, ULK, ELK, and/or XLK dielectric materials may comprise siliconoxide, silicon nitride, silicon oxynitride, spin-on glass (SOG),fluorinated silica glass (FSG), carbon doped silicon oxide (e.g.,SiCOH), Black Diamond® (Applied Materials of Santa Clara, Calif.),Xerogel, Aerogel, amorphous fluorinated carbon, Parylene, BCB(bis-benzocyclobutenes), Flare, SiLK (Dow Chemical, Midland, Mich.),polyimide, other proper porous polymeric materials, other suitabledielectric materials, and/or combinations thereof. The ILD layer 214 maybe formed by any suitable process, such as spin-on coating, chemicalvapor deposition (CVD), physical vapor deposition (PVD), atomic layerdeposition (ALD), high density plasma CVD (HPCVD), metal organic CVD(MOCVD), remote plasma CVD (RPCVD), plasma enhanced CVD (PECVD),sputtering, plating, other suitable processes, and/or combinationsthereof. In some embodiments, the ILD layer 214 may include a highdensity plasma (HDP) dielectric material and/or a high aspect ratioprocess (HARP) dielectric material. It is understood that the ILD layer214 may comprise one or more dielectric materials and/or one or moredielectric layers.

At step 104, a first conductive layer 216 is formed over the frontsurface of the substrate 210 in the first and second regions 211A, 211B,and in the present embodiment, over the ILD layer 214 to any suitablethickness. The first conductive layer 216 may comprise any suitablematerial, such as aluminum, copper, tungsten, titanium, tantulum,titanium nitride, tantalum nitride, nickel silicide, cobalt silicide,TaC, TaSiN, TaCN, TiAl, TiAlN, other proper conductive materials, and/orcombinations thereof. The first conductive layer 216 may be formed byany suitable process, such as spin-on coating, CVD, PVD, ALD, HPCVD,MOCVD, RPCVD, PECVD, sputtering, plating, other suitable processes,and/or combinations thereof. It is understood that the first conductivelayer 216 may comprise one or more materials.

Referring to FIG. 1 and FIGS. 2C-2F, at step 106, the first conductivelayer 216 is removed from the first region 211A. For example, in thepresent embodiment, removing the first conductive layer 216 in the firstregion 211A comprises forming a photoresist layer 218 over thesemiconductor device 200 as shown in FIG. 2C. The photoresist layer 218is patterned by a conventional photolithography process and/or processesto create one or more first portions 218A and one or more secondportions 218B as shown in FIG. 2D. The first portions 218A areunprotected portions. The second portions 218A are protected portionsthat may define a portion of the first metallization layer in the secondregion 211B, such as a portion of the bonding pad area. Then, the first,unprotected portions 218A of the photoresist layer 218 are etched awayand removed, along with the portions of the first conductive layer 216lying under the first, unprotected portions 218A of the photoresistlayer 218. As evident from FIG. 2E, the first conductive layer 216remains only under the second portions 218B of the photoresist layer218, defining a portion of the first metallization layer in the secondregion 211B, which defines the bonding pad area in the testing region ofthe semiconductor device 200. Subsequently, the photoresist layer 218(i.e., the remaining second portions 218B) may be removed. The firstconductive layer 216 defines the bonding pad area in the second region211B, the testing region, as shown in FIG. 2F.

It is understood that the first conductive layer 216 may be removed fromthe first region 211A using alone or in combination any of thephotolithography and/or etching processes described herein. Thephotolithography patterning process may include photoresist coating(e.g., spin-on coating), soft baking, mask aligning, exposure,post-exposure baking, developing the photoresist, rinsing, drying (e.g.,hard baking), other suitable processes, and/or combinations thereof. Thephotolithography exposing process may also be implemented or replaced byother proper methods such as maskless photolithography, electron-beamwriting, ion-beam writing, and molecular imprint. The etching processmay include dry etching, wet etching, and/or other etching methods(e.g., reactive ion etching). The etching process may also be eitherpurely chemical (plasma etching), purely physical (ion milling), and/orcombinations thereof. In some embodiments, a hard mask layer may beutilized to pattern and etch the first conductive layer 216.

At step 108, a second conductive layer 220 is formed over the substrate210 in the first and second regions 211A, 211B, and in the presentembodiment, over the first conductive layer 216. See, for example, FIG.2G. The second conductive layer 220 may comprise any suitable material,such as aluminum, copper, tungsten, titanium, tantulum, titaniumnitride, tantalum nitride, nickel silicide, cobalt silicide, TaC, TaSiN,TaCN, TiAl, TiAlN, other proper conductive materials, and/orcombinations thereof. The second conductive layer 216 may be formed byany suitable process, such as spin-on coating, CVD, PVD, ALD, HPCVD,MOCVD, RPCVD, PECVD, sputtering, plating, other suitable processes,and/or combinations thereof. It is understood that the second conductivelayer 220 may comprise one or more materials. In the present embodiment,the second conductive layer 220 comprises the same material as the firstconductive layer 216, but it is understood that, in alternateembodiments, the first conductive layer 216 and the second conductivelayer 220 may comprise different materials. The second conductive layer220 is any suitable thickness.

Referring to FIG. 1 and FIGS. 2H-2K, at step 110, portions of the secondconductive layer 220 are removed in the first and second regions 211A,211B, wherein the first region 211A M1,includes the first metallizationlayer M1 comprising the second conductive layer 220 and the M1,secondregion 211B includes the first metallization layer M1 comprising thefirst conductive layer 216 and the second conductive layer 220. Forexample, in the present embodiment, removing portions of the secondconductive layer 220 in the first and second regions 211A, 211Bcomprises forming a photoresist layer 222 over the semiconductor device200 as shown in FIG. 2H. The photoresist layer 222 is patterned by aconventional photolithography process and/or processes to create one ormore first portions 222A and one or more second portions 222B as shownin FIG. 2I. The first portions 222A are unprotected portions. The secondportions 222B are protected portions that define the first metallizationlayer in the first region 211A (i.e., define M1,a M1 layer of theintegrated circuit device area) and a portion of the first metallizationlayer in the second region 211B (e.g., a portion of the bonding padarea). Then, the first, unprotected portions 222A of the photoresistlayer 222 are etched away and removed, along with the portions of thesecond conductive layer 220 lying under the first, unprotected portions222A.

It is understood that the portions of the second conductive layer 220may be removed from the first and second regions 211A, 211B using aloneor in combination any of the photolithography and/or etching processesdescribed herein. The photolithography patterning process may includephotoresist coating (e.g., spin-on coating), soft baking, mask aligning,exposure, post-exposure baking, developing the photoresist, rinsing,drying (e.g., hard baking), other suitable processes, and/orcombinations thereof. The photolithography exposing process may also beimplemented or replaced by other proper methods such as masklessphotolithography, electron-beam writing, ion-beam writing, and molecularimprint. The etching process may include dry etching, wet etching,and/or other etching methods (e.g., reactive ion etching). The etchingprocess may also be either purely chemical (plasma etching), purelyphysical (ion milling), and/or combinations thereof. In someembodiments, a hard mask layer may be utilized to pattern and etch thesecond conductive layer 220.

As illustrated in FIG. 2J, the second conductive layer 220 remains onlyunder the M1,second portions 222B of the photoresist layer 222, definingthe first metallization layer M1 in the first and second regions 211A,211B. Subsequently, the photoresist layer 222 (i.e., the remainingsecond portions 222B) may be removed. Referring to FIG. 2K, the firstmetallization layer M1 M1,of the semiconductor device 200 is defined.The first metallization layer M1 in the first, integrated circuit deviceregion 211A comprises the second conductive layer 220, and the firstM1,metallization layer M1 in the second, testing region 211B comprisesthe first conductive layer M1,216 and the second conductive layer 220.The thickness of the first metallization layer M1 in the first region211A comprising the second conductive layer 220 is less than thethickness of the M1,first metallization layer M1 in the second region211B comprising the first conductive layer 216 and the second conductivelayer 220. Thus, the present embodiment provides the semiconductorM1,device 200 with the first metallization layer M1 in the second,testing region 211B (wherein a bonding pad may be formed) with anincreased thickness while maintaining the thickness of the M1,firstmetallization layer M1 in the first, integrated circuit device region211A. This is accomplished utilizing only one mask of the second,testing region 211B and one photolithography patterning and etchingprocess.

Referring to FIG. 1 and FIGS. 2L-2N, conventional processing may follow.For example, at step 112, one or more metallization layers are formedover the first metallization M1,layer M1. The one or more metallizationlayers comprise a plurality of metal structures 232, 242, 252. In thepresent embodiment, the semiconductor device 200 comprises fourM1,metallization layers, M1 through M4, metal structures comprisingfirst and second conductive M1,layers 216, 220 being M1, . . . metalstructures 242 being M(n−1) or M3, and metal structures 252 being thetopmost metal structure, M(N), or M4. Although only metal one (M1)through metal four (M4) metallization layers are illustrated, it isunderstood that the semiconductor device 200 may comprise any number ofmetallization layers, dependent on device complexity and design of theparticular device. For example, in some embodiments, the semiconductordevice 200 may comprise metallization layers M1 through M9. A pluralityof contact and/or via structures 222, 234, 244 and one or more ILDlayers 224, 230, 240, 250 are formed over the substrate 210. The ILDlayers 224, 230, 240, 250 separate and isolate each of the metallizationlayers and contact and/or via structures 222, 234, 244 from one another.The plurality of contact and/or via structures 222, 234, 244 may beconfigured to couple the substrate 210 to the metallization layersand/or metal structures and/or configured to couple one metal structureto another metal M1,structure, such as metal structure 232 to metalstructure 242, or metallization layer M2 to metallization layer M3, etc.

The metal structures 232, 242, 252; contact and/or via structures 222,234, 244; and ILD layers 224, 230, 240, 250 are formed by any suitableprocesses, such as the processes described herein. The metal structures232, 242, 252 may be similar to the first and second conductive layers216, 220. The contact/via structures 222, 234, 244 may comprise anysuitable material, such as aluminum, copper, tungsten, titanium,tantulum, titanium nitride, tantalum nitride, nickel silicide, cobaltsilicide, TaC, TaSiN, TaCN, TiAl, TiAlN, other proper conductivematerials, and/or combinations thereof. It is understood that each ofthe metal structures 232, 242, 252 and each of the conductive/viastructures 222, 234, 244 may comprise the same materials and/ordifferent materials. The ILD layers 224, 230, 240, 250 may comprisematerials similar to ILD layer 214, such as silicon oxide, siliconnitride, silicon oxynitride, SOG, FSG, SiCOH, Black Diamond® (AppliedMaterials of Santa Clara, Calif.), Xerogel, Aerogel, amorphousfluorinated carbon, Parylene, BCB, Flare, SiLK (Dow Chemical, Midland,Mich.), polyimide, other proper porous polymeric materials, othersuitable dielectric materials, and/or combinations thereof. It isunderstood that each of the ILD layers 224, 230, 240, 250 may compriseone or more dielectric materials and/or one or more dielectric layers.It is further understood that the ILD layers 224, 230, 240, 250 maycomprise the same materials and/or different materials.

As shown in FIG. 2L, a carrier wafer 260 may be bonded to the frontsurface of the substrate 210. The carrier wafer 260 may provideprotection for the various features formed on the front surface of thesubstrate 210. The carrier wafer 260 may also provide mechanicalstrength and support. The carrier wafer 260 may comprise any suitablematerial, such as silicon and/or glass. As discussed above, thesemiconductor device 200 includes sensor elements 212 that are formed onthe front surface of the substrate 210. Accordingly, the substrate 210may be processed to be made thin enough to allow the radiation incidenton the back surface of the substrate 210 to reach the sensor elements212. The substrate 210 may be thinned down from the back surface byvarious techniques as know in the art.

Then, referring to FIGS. 2M-2N, processing of the back surface of thesubstrate 210 may be performed. For example, various layers 270, 272(e.g., oxide layers) may be formed over the back surface of thesubstrate 210; and at step 114, an opening 280 is formed that extends toM1,the first metallization layer M1 in the second, testing region 211B.The various layers may comprise interfacial layers, dielectric layers,diffusion/barrier layers, conductive layers, capping layers, othersuitable layers, and/or combinations thereof. The opening 280 may beformed in the back surface of the substrate 210 using any suitableprocess, such as the processes described herein. For example, apatterned photoresist layer may be applied to the back surface of thesubstrate 210 and the opening 280 may be etched there-through. In thepresent embodiment, the M1,opening 280 is positioned directly over thefirst metallization layer M1 of the second, testing region 211Bcomprising the first and second conductive layers 216, 220 asillustrated in FIG. 2N. M1,Thus, the first metallization layer M1 of thesecond, testing region 211B comprising the first and second conductivelayers 216, 220 may be probed, or otherwise accessed, by a testingprobe. Such access allows testing measurements to be performed. In someembodiments, a bonding wire may be formed in the opening 280. Thebonding wire may comprise a barrier/diffusion layer and/or a conductivelayer. The bonding wire may further comprise any suitable material, suchas aluminum, copper, tungsten, titanium, tantulum, titanium nitride,tantalum nitride, nickel silicide, cobalt silicide, TaC, TaSiN, TaCN,TiAl, TiAlN, other proper conductive materials, and/or combinationsthereof.

It is understood that additional features may be formed over the backsurface of the substrate 210. For example, the semiconductor device 200may further comprises a color filter layer that supports severaldifferent color filters (e.g., red, green, and blue). The color filtersmay correspond to the various sensor devices 212 on the substrate 210.The semiconductor device 200 may further comprise a plurality of lenses,such as microlenses, in various positional arrangements with sensordevices 212 and/or color filters, such that incident light may befocused on the light-sensing regions. Other proper imaging features mayfurther be formed on the back surface of the substrate 210.

In summary, the disclosed embodiments provide a method for fabricating abackside illuminated sensor device comprising providing a substratehaving a front surface and a back surface; forming one or more sensorelements on the front surface of the substrate; and forming one or moremetallization layers over the front surface of the substrate, wherein athickness of a first metallization layer in a testing area/region isthicker than the thickness of the first metallization layer in anintegrated circuit device area/region. The method provides one mask andone pattering/etching step to increase the thickness of the firstmetallization layer in the testing region, while maintaining thethickness of the first metallization layer in the integrated circuitdevice region at an original thickness. The disclosed embodimentsimprove bonding ability.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. A semiconductor device, comprising: a substrate having a frontsurface, a back surface, a first region, a second region, and one ormore sensor elements; an interlayer dielectric (ILD) layer on thesubstrate; and a first metal layer on the ILD layer, wherein the firstmetal layer comprises a first conductive layer on the ILD layer and asecond conductive layer on the first conductive layer in the secondregion, and the first metal layer comprises the second conductive layerdirectly on the ILD layer in the first region.
 2. The semiconductordevice of claim 1, further comprising an opening that extends from theback surface of the substrate to the first metal layer in the secondregion.
 3. The semiconductor device of claim 1, wherein the first regioncomprises an integrated circuit device and the second region comprises atesting area.
 4. The semiconductor device of claim 1, wherein thethickness of the first metal layer in the first region is less than thethickness of the first metal layer in the second region.
 5. Thesemiconductor device of claim 1, further comprising one or moreinter-level dielectric layers and one or more contact and/or viastructures on the substrate.
 6. The semiconductor device of claim 1,further comprising a carrier wafer on the front surface of thesubstrate.
 7. The semiconductor device of claim 1, wherein the first andsecond conductive layers comprise the same material.
 8. A semiconductordevice, comprising: a substrate having a front surface and a backsurface; an interlayer dielectric (ILD) layer on the substrate; a firstmetal layer in a first region of the substrate, the first metal layer inthe first region comprising a conductive layer in direct contact withthe ILD layer; a first metal layer in a second region of the substrate,the first metal layer in the second region comprising a first conductivelayer on the ILD layer and a second conductive layer over the firstconductive layer; and one or more sensor elements on the first region ofthe substrate that are proximate to the back surface of the substrate.9. The semiconductor device of claim 8, further comprising an openingthat extends from the back surface of the substrate to the first metallayer in the second region.
 10. The semiconductor device of claim 8,wherein the first region comprises an integrated circuit device and thesecond region comprises a testing area.
 11. The semiconductor device ofclaim 8, wherein the thickness of the first metal layer in the firstregion is less than the thickness of the first metal layer in the secondregion.
 12. The semiconductor device of claim 8, further comprising oneor more inter-level dielectric layers and one or more contact and/or viastructures on the substrate.
 13. The semiconductor device of claim 8,further comprising a carrier wafer on the front surface of thesubstrate.
 14. A semiconductor device, comprising: a substrate having afront surface and a back surface; one or more sensor elements on thesubstrate; an interlayer dielectric (ILD) layer on the substrate; afirst metal layer on the ILD layer having a first thickness in a firstregion of the substrate and a second thickness in a second region of thesubstrate, wherein the second thickness is greater than the firstthickness, wherein the first metal layer in the second region comprisesa first conductive layer on the ILD layer and a second conductive layeron the first conductive layer, and the first metal layer in the firstregion comprises the second conductive layer directly on the ILD layer.15. The semiconductor device of claim 14, further comprising an openingthat extends from the back surface of the substrate to the first metallayer in the second region.
 16. The semiconductor device of claim 14,wherein the first region comprises an integrated circuit device and thesecond region comprises a testing area.
 17. The semiconductor device ofclaim 14, further comprising one or more inter-level dielectric layersand one or more contact and/or via structures on the substrate.
 18. Thesemiconductor device of claim 14, further comprising a carrier wafer onthe front surface of the substrate.
 19. The semiconductor device ofclaim 14, wherein the one or more sensor elements are on the firstregion of the substrate and are proximate to the back surface of thesubstrate.
 20. The semiconductor device of claim 14, wherein the firstand second conductive layers comprise the same material.